1. Field of the Invention
The invention relates in general to a concealed antenna, and more particularly to a concealed antenna mounted directly on the motherboard of a notebook computer.
2. Description of the Related Art
In a wireless communication system, such as a notebook computer or a mobile phone, an antenna is a device for transmitting and receiving electromagnetic waves. The way that an antenna is designed and the location that it is mounted in the system influences its radiation field pattern, and the quality of signal transmission. Furthermore, how the antenna is configured in the system will have a great effect on the cost of manufacturing the whole system.
Referring to FIG. 1, a schematic view of a conventional notebook computer equipped with a concealed antenna is shown. A notebook computer 100 generally includes a liquid crystal display (LCD) 110 and a base module 120. Two concealed antennas 130 are symmetrically configured to the center of the upper edge of the LCD 110 to enhance the antenna diversity. A RF coaxial cable 132 is provided as a feed-in line of the antenna 130 so that the RF signals can be transmitted between the antenna 130 and the RF module 140 on the base module 120. A sheet of shielding aluminum foil 134 is electrically coupled with the antenna 130 to improve the antenna radiation performance.
However, the above-mentioned structure of the antenna 130 equipped with the RF coaxial cable 132 for transmitting RF signals has the following disadvantages:
1. Insertion loss: for a 100-centimeter-long high quality RF coaxial cable in the market, the insertion loss is 2.9 dB as the RF signal frequency is 2.4 GHz while the insertion loss is 4.7 dB as the RF signal frequency is 5 GHz. Generally, the length of a RF coaxial cable used in the notebook computer is about 20 cm to 90 cm. Therefore, the insertion loss is about 0.58 dB to 2.61 dB as the RF coaxial cable transmits a 2.4 GHz signal while the insertion loss goes up to 0.94 dB to 4.23 dB as the RF coaxial transmits a 5 GHz signal. Owing to the insertion loss, the antenna field pattern has to be concentrated to provide enough antenna gain for transmitting signals to a given distance. As a result, antenna radiation angles will be reduced and dead space in communication will be increased, which directly reduces communication quality.
2. Cost increase: according to the general estimation conducted by antenna manufacturing industry, the above-mentioned RF coaxial cable occupies about 50% of the antenna manufacturing cost. Moreover, as the wireless system is fabricated, additional devices, such as hooks for fixing the RF coaxial cable and fixing pieces for fixing the shielding aluminum foil, are required to fix the RF coaxial cable, which further increases the cost. The labor hours for configuring and positioning the RF coaxial cable will largely increase the fabrication cost.